¹Connor Brolly, ¹John Parnell, ¹Stephen Bowden
¹Department of Geology & Petroleum Geology, University of Aberdeen, Aberdeen, UK

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Reference
Brolly C, Parnell J, Bowden S (2016) Raman spectroscopy: Caution when interpreting organic carbon from oxidising Environments. Planetary and Space Science 121, 53–59
Link to Article [doi:10.1016/j.pss.2015.12.008]

¹Karel Žák, ¹Roman Skála, ²Zdeněk Řanda, ²Jiří Mizera, ³Kurt Heissig,, ¹Lukáš Ackerman, ¹Jana Ďurišová, ¹Šárka Jonášová, ²Jan Kameník, ⁴Tomáš Magna
¹Institute of Geology, The Czech Academy of Sciences, Rozvojová 269, CZ-165 00 Prague 6, Czech Republic
²Nuclear Physics Institute, The Czech Academy of Sciences, Hlavní 130, CZ-250 68 Husinec-Řež, Czech Republic
³Bayerische Staatssammlungen für Paläontologie und Geologie, Paläontolgisches Museum, Richard-Wagner-Straße 10, D-80333 München, Germany
⁴Czech Geological Survey, Klárov 3, CZ-118 21 Prague 1, Czech Republic

Moldavites, tektites of the Central European strewn field, have been traditionally linked with the Ries impact structure in Germany. They are supposed to be derived mainly from the near-surface sediments of the Upper Freshwater Molasse of Miocene age that probably covered the target area before the impact. Comparison of the chemical composition of moldavites with that of inferred source materials requires recalculation of the composition of sediments to their water-, organic carbon- and carbon dioxide-free residuum. This recalculation reflects the fact that these compounds were lost almost completely from the target materials during their transformation to moldavites. Strong depletions in concentrations of many elements in moldavites relative to the source sediments (e.g., Mo, Cu, Ag, Sb, As, Fe) are contrasted with enrichments of several elements in moldavites (e.g., Cs, Ba, K, Rb). These discrepancies can be generally solved using two different approaches, either by involvement of a component of specific chemical composition, or by considering elemental fractionation during tektite formation. The proposed conceptual model of moldavite formation combines both approaches and is based on several steps: (i) the parent mixture (Upper Freshwater Molasse sediments as the dominant source) contained also a minor admixture of organic matter and soils; (ii) the most energetic part of the ejected matter was converted to vapor (plasma) and another part produced melt directly upon decompression; (iii) following further adiabatic decompression, the expanding vapor phase disintegrated the melt into small melt droplets and some elements were partially lost from the melt because of their volatility, or because of the volatility of their compounds, such as carbonyls of Fe and other transition metals (e.g., Ni, Co, Mo, Cr, and Cu); (iv) large positively charged ions such as Cs+, Ba2+, K+, Rb+ from the plasma portion were enriched in the late-stage condensation spherules or condensed directly onto negatively charged melt droplets; (v) simultaneously, the melt droplets coalesced into larger tektite bodies. Steps (iii) to (v) may have overlapped in time. The still melted moldavite bodies reaching their final size were reshaped by further melt flow. This melt flow was related to moldavite rotation and escape (bubbling off) of the last portion of gaseous volatiles during their flight in a low-pressure region above the dense layer of the atmosphere.

Reference
Žák K, Skála R, Řanda Z, Mizera J, Heissig K, Ackerman L, Ďurišová J, Jonášová Š, Kameník J,  Magna T (2016) Chemistry of Tertiary sediments in the surroundings of the Ries impact structure and moldavite formation revisited. Geochmica et Cosmochimcia Acta (in Press)
Link to Article [doi:10.1016/j.gca.2016.01.025]
Copyright Elsevier

¹Samuel Ebert, ¹Addi Bischoff
¹Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany

Al-rich objects (Ca,Al-rich inclusions (CAIs), Al-rich chondrules, Al-rich fragments) occur in all chondrite classes. These objects can be centimeter-sized in CV3 carbonaceous chondrites, but they are generally much smaller in other chondrite groups and classes. Within the ordinary chondrites, most Al-rich objects are chondrules that vary from Ca- to Na-rich. Here, we have investigated the mineralogy and major element chemistry of 32 Na-rich chondrules and 3 Na-rich fragments from 15 different chondrites. Most objects (chondrules and chondrule fragments) are from ordinary chondrites (petrologic types 3.2-3.8), but two of the chondrules are from two CO3 chondrites, and three of the chondrules are from one Rumuruti (R)-chondrite. We found that these Na-rich objects have bulk Na2O-concentrations between 4.3 and 15.2 wt%. Texturally, they typically consist of euhedral to subhedral (often skeletal) mafic minerals (olivine and pyroxenes) embedded within a nepheline-normative, glassy mesostasis, which is brownish in transmitted light. In addition, some chondrules contain euhedral to subhedral spinel. Bulk chondrule compositions show group II, group III, and ultrarefractory rare earth element (REE) patterns similar to those found in CAIs. These results clearly demonstrate that the Na-rich chondrules must have been formed by melting of precursors containing an (ultra)-refractory element-rich component and Na-rich constituents. The Na-rich chondrules showed Sm and Eu anomalies, indicating that they must have formed at low oxygen fugacities. Based on the chemical composition of the Na-rich objects, we can rule out that they were formed as a result of planetary formation due to metasomatic processes or processes related to collisions between molten planetesimals.

Reference
Ebert S, Bischoff A (2016) Genetic relationship between Na-rich chondrules and Ca,Al-rich inclusions? – Formation of Na-rich chondrules by melting of refractory and volatile precursors in the Solar Nebula. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2016.01.014]
Copyright Elsevier

^1,2Myriam Telus, ²Gary R. Huss, ³Ryan C. Ogliore, ^1,2Kazuhide Nagashima, ³Daryl L. Howard, ⁴Matthew G. Newville, ⁵Andrew G. Tomkins
¹Geology & Geophysics, School of Ocean, Earth Science & Technology, University of Hawai‘i at Mānoa, Honolulu, HI 96822, USA
²Hawai‘i Institute of Geophysics and Planetology, School of Ocean, Earth Science & Technology, University of Hawai‘i at Mānoa, Honolulu, HI 96822, USA
³Australian Synchrotron, Clayton, Victoria 3168, Australia
⁴Center for Advanced Radiation Sources, University of Chicago, Chicago, IL 60637, USA
⁵School of Earth, Atmosphere & Environment, Monash University, Melbourne, Victoria 3800, Australia

The Fe and Ni isotopic composition of ferromagnesian silicates in chondrules from unequilibrated ordinary chondrites (UOCs) have been used to estimate the initial abundance of the short-lived radionuclide, 60Fe, in the early Solar System. However, these estimates vary widely, and there are systematic discrepancies in initial 60Fe/56Fe ratios inferred from in situ and bulk analyses of chondrules. A possible explanation is that the Fe-Ni isotope system in UOC chondrules has not remained closed (a necessary condition for isotopic dating), and Fe and Ni have been redistributed since the chondrules formed. In order to evaluate this, we collected high-spatial-resolution X-ray fluorescence (XRF) maps of UOC chondrules to better understand the distribution and mobility of Fe and Ni at the low metamorphic temperatures of these chondrites. We used synchrotron X-ray-fluorescence microscopy to map the distribution of Fe, Ni and other elements in portions of 71 chondrules from 8 UOCs (types 3.00-3.2). The synchrotron XRF maps show clear enrichment of Fe and/or Ni in fractures ranging down to micrometer scale in chondrules from all UOCs analyzed for this study regardless of petrologic type and regardless of whether fall or find, indicating that there was significant exchange of Fe and Ni between chondrules and matrix and that the Fe-Ni system was not closed. Sixty percent of chondrules in Semarkona (LL3.00) have Fe and Ni enrichment along fractures, while 80-100% of chondrules analyzed from the other UOCs show these enrichments. Mobilization was likely a result of fluid transport of Fe and Ni during aqueous alteration on the parent body and/or during terrestrial weathering. In situ and bulk Fe-Ni analyses that incorporate extraneous Fe and Ni from chondrule fractures will result in lowering the inferred initial 60Fe/56Fe ratios.

Reference
Telus M, Huss GR, Ogliore RC, Nagashima K, Howard DL, Newville MG, Tomkins AG (2016) Mobility of Iron and Nickel at Low Temperatures: Implications for 60Fe-60Ni Systematics of Chondrules from Unequilibrated Ordinary Chondrites. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.11.046]
Copyright Elsevier

The most popular papers on Cosmochemistry Papers in January were:

1-Chan QHS, Chikaraishi Y, Takano Y, Ogawa NO, Ohkouchi N (2016) Amino acid compositions in heated carbonaceous chondrites and their compound-specific nitrogen isotopic ratios. Earth, Planets and Space 68, 7
Link to Article [doi:10.1186/s40623-016-0382-8]

2-Steenstra ES, Knibbe JS, Rai N, van Westrenen W (2016) Constraints on core formation in Vesta from metal–silicate partitioning of siderophile elements. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2016.01.002]

3-Heck PR, Schmitz B, Rout SS, Tenner T, Villalon K, Cronholm A, Terfelt F,Kitae NT (2016) A search for H-chondritic chromite grains in sediments that formed immediately after the breakup of the L-chondrite parent body 470 Ma ago. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.11.042]

4-Friedrich JM,Glavin DP,Rivers ML, Dworkin JP (2016) Effect of a synchrotron X-ray microtomography imaging experiment on the amino acid content of a CM chondrite. Meteoritics & Planetary Sciences (in Press)
Link to Article [DOI: 10.1111/maps.12595]

5-Haggerty SE (2016) Spinel in planetary systems. American Mineralogist 101,5-6
Link to Article[doi:10.2138/am-2016-5554]

¹Edward D. Young, ¹Issaku E. Kohl, ¹Paul H. Warren, ²David C. Rubie, ^2,3Seth A. Jacobson, ³Alessandro Morbidelli
¹Department of Earth, Planetary, and Space Sciences, University of California Los Angeles, Los Angeles, CA, USA.
²Bayerisches Geoinstitut, University of Bayreuth, D-95490 Bayreuth, Germany.
³Laboratoire Lagrange, Université de Nice–Sophia Antipolis, Observatoire de la Cote d’Azur, CNRS, 06304 Nice, France.

Earth and the Moon are shown here to have indistinguishable oxygen isotope ratios, with a difference in Δ′17O of −1 ± 5 parts per million (2 standard error). On the basis of these data and our new planet formation simulations that include a realistic model for primordial oxygen isotopic reservoirs, our results favor vigorous mixing during the giant impact and therefore a high-energy, high-angular-momentum impact. The results indicate that the late veneer impactors had an average Δ′17O within approximately 1 per mil of the terrestrial value, limiting possible sources for this late addition of mass to the Earth-Moon system.

Reference
Young ED,Kohl IE,Warren PH,Rubie DC,Jacobson SA,Morbidelli A (2016) Oxygen isotopic evidence for vigorous mixing during the Moon-forming giant impact. Science 351, 6272, 493-496
Link to Article [DOI: 10.1126/science.aad0525]
Reprinted with permission from AAAS

¹Y. Langevin et al. (>10)*
¹Institut d’Astrophysique Spatiale, CNRS/Univ. Paris-Sud, Orsay, France
*Find the extensive, full author and affiliation list on the publishers website

The COSIMA mass spectrometer on board the ROSETTA orbiter has collected dust in the near coma of comet 67P/Churyumov-Gerasimenko since August 11, 2014. The collected dust particles are identified by taking images with a microscope (COSISCOPE) under grazing incidence illumination before and after exposure of the target to cometary dust. More than 10,000 dust particles > 14 µm in size collected from August 11, 2014 to April 3, 2015 have been detected on three distinct target assemblies, including ∼ 500 dust particles with sizes ranging from 50 to more than 500 µm, that can be resolved by COSISCOPE (pixel size 14 µm). During this period, the heliocentric distance decreased from 3.5 AU to less than 2 AU. The collection efficiency on targets covered with “metal black” has been very high, due to the low relative velocity of incoming dust. Therefore, the COSISCOPE observations provide the first optical characterization of an unbiased sample of particles collected in the inner coma of a comet. The typology of particles > 100 µm in size is dominated by clusters with a wide range of structure and strength, most originating from the disruption of large aggregates (> 1 mm in size) shortly before collection. A generic relationship between these clusters and IDPs / Antarctic meteorites is likely in the framework of accretion models. About 15% of particles larger than 100 µm are compact particles with two likely contributions, one being linked to clusters and another leaving the cometary nucleus as single compact particles.

Reference
Langevin Y et al. (2016) Typology of dust particles collected by the COSIMA mass spectrometer in the inner coma of 67P/Churyumov Gerasimenko. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.01.027]
Copyright Elsevier

¹O. Pravdivtseva, ¹A. Meshik, ¹C.M. Hohenberg,²A.N. Krot
¹Physics Department, Washington University, St. Louis MO 63130, USA
²Hawai‘i Institute of Geophysics and Planetology, School of Ocean, Earth Science and Technology, University of Hawai’i at Mānoa, Honolulu, HI 96822, USA

It is inferred that magnesian non-porphyritic chondrules in the CB (Bencubbin-type) carbonaceous chondrites formed in an impact generated plume of gas and melt 4562.49 ± 0.21 Ma (Bollard et al., 2015) and could be suitable for the absolute age normalization of relative chronometers. Here xenon isotopic compositions of neutron irradiated chondrules from the CB chondrites Gujba and Hammadah al Hamra (HH) 237 have been analyzed in an attempt to determine closure time of their I-Xe isotope systematics. One of the HH 237 chondrules, #1, yielded a well-defined I-Xe isochron that corresponds to a closure time of 0.29 ± 0.16 Ma after the Shallowater aubrite standard. Release profiles and diffusion properties of radiogenic 129∗Xe and 128∗Xe extracted from this chondrule by step-wise pyrolysis, indicate presence of two iodine host phases with distinct activation energies of 73 and 120 kcal/mol. In spite of the activation energy differences, the I-Xe isotope systematics of these two phases closed simultaneously, suggesting rapid heating and cooling (possibly quenching) of the CB chondrules. The release profiles of U-fission Xe and I-derived Xe correlate in the high temperature host phase supporting simultaneous closure of 129I-129Xe and 207Pb-206Pb systematics.

The absolute I-Xe age of Shallowater standard is derived from the observed correlation between I-Xe and Pb-Pb ages in a number of samples. It is re-evaluated here using Pb-Pb ages adjusted for an updated 238U/235U ratio of 137.794 and meteorite specific U-isotope ratios. With the addition of the new data for HH 237 chondrule #1, the re-evaluated absolute I-Xe age of Shallowater is 4562.4 ± 0.2 Ma. The absolute I-Xe age of the HH 237 chondrule #1 is 4562.1 ± 0.3 Ma, in good agreement with U-corrected Pb-Pb ages of the Gujba chondrules (Bollard et al., 2015) and HH 237 silicates (Krot et al., 2005).

All I-Xe data used here, and in previous estimates of the absolute age of Shallowater, are calculated using 15.7 ± 0.6 Ma value for 129I half-life. The slopes of I-Xe – Pb-Pb correlation lines plotted for different sets of samples for Shallowater normalization are always ⩽ 1. Assuming uranium half-life values are correct; this restricts the half-life of 129I to ⩽ 15.7 Ma.

Reference
Pravdivtseva O, Meshik A, Hohenberg CM, Krot AN (2016) I-Xe systematics of the impact plume produced chondrules from the CB carbonaceous chondrites: Implications for the half-life value of 129I and absolute age normalization of 129I-129Xe chronometer. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2016.01.012]
Copyright Elsevier

¹Noriyuki Kawasaki, ²Shoichi Itoh, ³Naoya Sakamoto, ¹Hisayoshi Yurimoto
¹Department of Natural History Sciences, Hokkaido University, Sapporo 060-0810, Japan
²Department of Earth and Planetary Sciences, Kyoto University, Kyoto 606-8502, Japan
³Creative Research Institution, Hokkaido University, Sapporo 001-0021, Japan

Fluffy Type A Ca-Al-rich inclusions (CAIs) containing reversely zoned melilite crystals are suggested to be direct condensates from solar nebular gas. We conducted an investigation of 26Al−26Mg systematics of a fluffy Type A CAI from Vigarano, named V2-01, with known oxygen isotopic distributions of reversely zoned melilite crystals; we also conducted oxygen isotope measurements of coexisting minerals. Two of six reversely zoned melilite crystals show continuous variations in magnesium isotopic composition, with δ25Mg becoming small along the inferred direction of crystal growth, which supports the idea that they originated through condensation. Petrography suggests that the constituent minerals of V2-01 formed in the following order: first spinel and fassaite enclosed by melilite, then reversely zoned melilite crystals, and spinel and diopside in the Wark-Lovering rim. The spinel enclosed by melilite has 16O-rich compositions (Δ17O ∼ −24‰) and an initial value of (26Al/27Al)0 = (5.6 ± 0.2) × 10−5. The fassaite enclosed by melilite crystals shows variable oxygen isotopic compositions (Δ17O ∼ −12‰ and −17‰) and plots on an isochron with (26Al/27Al)0 = (5.6 ± 0.2) × 10−5. The oxygen isotopic compositions of reversely zoned melilite showed continuous variations in Δ17O along the inferred direction of crystal growth, suggesting that surrounding nebular gas, during the formation of the reversely zoned melilite, changed from 16O-poor (Δ17O values larger than −10‰) to 16O-rich (Δ17O ∼ −25‰). The six reversely zoned melilite crystals show indistinguishable initial 26Al/27Al values with an average (26Al/27Al)0 of (4.7 ± 0.3) × 10−5, which is clearly distinguishable from the value of enclosed spinel and fassaite, indicating a younger formation age than the enclosed spinel and fassaite. The spinel and diopside from the Wark-Lovering rim shows 16O-rich compositions (Δ17O ∼ −23‰) with (26Al/27Al)0 = (4.5 ± 0.4) × 10−5. The values of (26Al/27Al)0 are consistent with the formation sequence inferred from petrography. The formation period for the V2-01 CAI is estimated to be 0.18 ± 0.07 Myr from the difference in initial 26Al/27Al values. These data suggest that the oxygen isotopic composition of solar nebular gas surrounding the CAI changed from 16O-rich to 16O-poor and back to 16O-rich during the first ∼0.2 Myr of Solar System formation.

Reference
Kawasaki N,Itoh S,Sakamoto N, Yurimoto H (2016) Chronological study of oxygen isotope composition for the solar protoplanetary disk recorded in a fluffy Type A CAI from Vigarano. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.12.031]
Copyright Elsevier

¹J. P. Das, ¹S. L. Baldwin, ²J. W. Delano
¹Department of Earth Sciences, Syracuse University, Syracuse 13244, NY, USA
²Department of Atmospheric and Environmental Sciences, University of Albany (SUNY), Albany 12222, NY, USA

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Reference
Das JP, Baldwin SL, Delano JW (2016) 40 Ar/ 39 Ar and cosmic ray exposure ages of plagioclase-rich lithic fragments from Apollo 17 regolith, 78461. Earth, Planets and Space 68, 11
Link to Article [doi:10.1186/s40623-016-0381-9]